1. Field
The present invention relates to the manufacture of a molding element by sintering and more particularly to the manufacture of a molding element intended to be arranged in a mold for tires, notably a mold of the segmented type.
2. Description of Related Art
A segmented mold comprises several separate pieces which, by being brought closer together, delimit a molding space of toroidal overall shape. In particular, a segmented mold comprises two lateral shells for molding the sidewalls of the tire and several peripheral segments situated between the shells for molding the tread of the tire. All of these pieces are brought mutually closer together by suitable kinematics, using a determined mechanism.
In order to mold the tread, the mold segments comprise molding elements. A molding element means any element of the mold which comprises a molding surface that allows part of the tread of a tire to be molded. A molding element may therefore be a block assembled on a mold segment or a protrusion, such as a blade or a strip, attached to the radially interior surface of the mold.
It is possible to create a molding element by a selective fusion method more commonly referred to as sintering. This method uses a beam of energy to fuse a metallic powder. A “beam of energy” means electromagnetic radiation (for example a laser beam) or a beam of particles (for example a beam of electrons).
A sintering method that employs a laser, hereinafter referred to as a laser sintering method, is known from document EP 1 641 580. In that document, a first layer of metallic powder is spread on a plate. All or some of the particles of this first layer of powder are then agglomerated by the beam of a laser according to the shape of the object that is to be obtained. Once this step has been carried out, a second layer of powder is spread over the first layer of powder and is in its turn selectively fused by laser. By repeating these operations of spreading a layer and fusing it using a laser a sintered object is built up layer by layer.
Laser fusing generates thermal expansions within the sintered object and this causes stresses to appear after the object has returned to ambient temperature. When the sintered object is detached from the support plate, for example during a rapid cutting using a wire, stresses cause the sintered object to deform. If the sintered object is a solid object then such deformations are even more extensive.
In order to limit such deformations, document WO 2010/076503 discloses a molding element produced by laser sintering that has a particular internal arrangement. The molding element thus comprises a fine shell delimiting an interior volume and a core internal to the shell. The shell is solid and the internal core has a meshed structure comprising a plurality of cavities. To improve the thermal conductivity of the molding element, the cavities of the core are filled with non-fused metallic powder.
Although the molding element of document WO 2010/076503 exhibits less deformation when detached from a support plate, there are still concentrations of stresses in the region of the shell. The operation of detaching the molding element from the support plate therefore leads to some degree of deformation of the shell and, in certain extreme cases of deformation, cracks may appear in this shell. It is thus possible for non-fused powder to escape from these cracks, then leading to a risk of contaminating the tooling and therefore the molded tires and leading to a risk of this powder being inhaled by an operator handling the molding element.
Document DE 10 2004 028 462 discloses a molding element comprising a sintered part and a non-sintered part attached to this sintered part. The non-sintered part has a junction surface where it joins the non-sintered part which is completely flat thus preventing the use of the sintering method as disclosed in document EP 1 641 580.
There is therefore a need to offer a method for manufacturing a molding element by laser sintering which is simple and economical and guarantees limited deformation of this molding element after it has been manufactured and a high level of safety with respect to any non-fused powder present in the molding element.